1. Field of the Invention
The present invention relates to a system and method for controlling auto-ignition of a four-stroke gasoline internal combustion (IC) engine, and an auto-ignition type IC engine.
2. Description of Related Art
JP-A 10-266878 discloses a technique to accomplish auto-ignition of gasoline fuel over a predetermined load range from low load to middle load by adjusting closing timing of an exhaust valve as well as opening and closing timings of an intake valve. According to this known technique, over the predetermined load range, an opening timing of the exhaust valve is held invariable at a crank position before a bottom dead center (BDC) position of expansion stroke against variations of load request, but a closing timing of the exhaust valve is adjusted to varying crank positions before a top dead center (TDC) position of exhaust stroke against varying load request. A throttle valve is fully opened over this predetermined load range. The closing timing of the exhaust valve advances as load request becomes low to increase the amount of exhaust gas remaining in a cylinder to decrease the amount of fresh charge. In order to retain exhaust gas, the opening timing of the intake valve is adjusted to varying crank positions after the TDC position of exhaust stroke against varying load request over the predetermined load range. The opening timing of the intake valve retards as load request becomes low. The closing timing of the intake valve is adjusted to varying crank positions after a bottom dead center (BDC) position of intake stroke against varying load request over the predetermined load range. The closing timing of the intake valve retards gradually as load request becomes high over a portion of the predetermined load range and then advances gradually as load request becomes high over the remaining portion of the predetermined load range. According to this known technique, closing timing of the exhaust valve controls the amount of exhaust gas in the cylinder, thereby controlling available combustion chamber volume for receiving fuel mixture thereby controlling load. Further, closing timing of the intake valve advances during operation with load where auto-ignition is difficult to accomplish. Advancing closing timing of intake valve increases a compression ratio thereby increasing temperature of the mixture in the cylinder.
The known technique is satisfactory to some extent, however, involves a potential problem that auto-ignition might not be sustained against variation of temperature conditions in the cylinder. The variation of temperature conditions include a change in cylinder wall temperature during transient operation of the engine at warming-up or acceleration, and a cyclic change in cylinder wall temperature due to a change in intake air temperature, a cycle-by-cycle variation of intake air amount, and a cycle-by-cycle variation of fuel injection amount. It is known that, with the same load request, advancing closing timing of exhaust valve causes an increase in temperature in cylinder thereby sustaining auto-ignition against an undesired drop in cylinder wall temperature. However, if closing timing of exhaust valve is always advanced in the above manner to retain sufficient amount of exhaust gas to deal with the undesired drop in cylinder wall temperature, the temperature in the cylinder is always elevated, inducing cooling loss thereby deteriorating fuel economy.
Thus, there would be a need for fine and accurate control of exhaust gas retaining phase to accomplish auto-ignition and to minimize cooling loss as well.
An object of the present invention is to control auto-ignition to meet the above-mentioned need.
In one aspect of the present invention, the above object is achieved by an auto-ignition type internal combustion engine, which comprises at least one cylinder, an inlet control device for controlling flow into the cylinder, an outlet control device for controlling flow from the cylinder, a fuel injection device for supplying gasoline fuel into the cylinder, a generator for providing a parameter indicative of combustion event within the cylinder, and an engine controller for adjusting the inlet and outlet control devices to retain exhaust gas for subjecting the retained exhaust gas to compression and varying at least closing timing of the outlet control device based on the parameter.